The present invention relates to layer 2 and layer 3 switching of data packets in a network switch configured for switching data packets between and within subnetworks.
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface devices at each network node to access the network medium.
The Ethernet protocol IEEE 802.3 has evolved to specify a half-duplex media access mechanism and a full-duplex media access mechanism for transmission of data packets. The full-duplex media access mechanism provides a two-way, point-to-point communication link between two network elements, for example between a network node and a network switch.
Switched local area networks are encountering increasing demands for higher speed connectivity, more flexible switching performance, and the ability to accommodate more complex network architectures. For example, commonly-assigned U.S. Pat. No. 5,953,335 discloses a network switch configured for switching layer 2 type Ethernet (IEEE 802.3) data packets between different network nodes; a received data packet may include a VLAN (virtual LAN) tagged frame according to IEEE 802.1q protocol that specifies another subnetwork (via a router) or a prescribed group of stations. Since the switching occurs at the layer 2 level, a router is typically necessary to transfer the data packet between subnetworks.
One example of the increased demand encountered by switched local area networks includes data transport of media streams for multimedia applications having quality of service requirements between a media source and a host computer configured as a receiver for a user. In particular, the Internet Engineering Task Force (IETF) Resource Reservation Setup Protocol Working Group has proposed a new standard (RFC 2205), entitled the Resource Reservation Protocol (RSVP), for setting up resource reservations in the Internet. The RSVP protocol can be used by a host receiver to request from a router, located along a path between a media source (i.e., a sender) and the host receiver, a specific quality of service (i.e., a guaranteed bandwidth) for a particular application in order to guarantee a quality of service from the sender to the receiver. The RSVP protocol can also be used by the routers to deliver the quality of service request to all nodes along the path and to establish and maintain state to provide the requested service.
For example, assume that a user at an end station wishes to enjoy reception of a high-quality video stream from a media source via the Internet. Assuming that the end station is a member of an Internet Group Management Protocol (IGMP) multicast group, the end station needs to send a bandwidth reservation (Resv) message to its local router according to the RSVP protocol to request bandwidth for an assured quality of service. The local router, in response to receiving the bandwidth reservation message, checks to see whether the end station is authorized to request the specified bandwidth. If the local router determines that the end station is not authorized to request the specified bandwidth, the local router returns a message denying the request to the end station; however if the local router determines that the end station is authorized to request the specified bandwidth, the local router forwards the request to the next router in the hop sequence toward the media source, enabling each router in the path between the media source and the end station to reserve bandwidth for the quality of service requested by the end station.
The above-described arrangement for requesting quality of service according to the RSVP protocol suffers from the disadvantage that the local router may approve the bandwidth request from the end station, even though a layer 2/layer 3 switch configured for switching data packets between the end station and the router does not have sufficient capacity to support the requested quality of service. Specifically, during the bandwidth reservation according to RSVP protocol there is no protocol exchange between the end station and the layer 2/layer 3 switch, nor between the layer 2/layer 3 switch and the local router. Hence, there is no means for the layer 2/layer 3 switch to send a message to either the end station or the local router if the layer 2/layer 3 switch is unable to support the bandwidth request.
There is a need for an arrangement that enables a network switch to provide layer 2 switching and layer 3 switching capabilities while supporting prescribed quality of service requirements.
There is also a need for an arrangement that enables a network switch to be easily programmable to identify data packets carrying bandwidth reservation messages so that quality of service (QoS) can be achieved.
There is also a need for an arrangement to enable a network switch to evaluate an incoming data packet having a bandwidth reservation message and determine whether the network switch is able to support the requested bandwidth.
These and other needs are attained by the present invention, where a network switch is configured for selectively changing a requested quality of service in a bandwidth reservation message, output from a host computer for reception by a router, based on a determined absence of available resources within the network switch. The network switch selectively increases the requested quality service, based on the determined absence of the available resources, to a value that will be denied by the router. Hence, the network switch can ensure that a router does not grant a bandwidth reservation message from a host computer that would cause the capacity of the network switch to be exceeded.
One aspect of the present invention provides a method in a network switching system. The method includes receiving by a network switching system a data packet from a host computer and having a media access control (MAC) destination address specifying a router. The method also includes detecting within the data packet a bandwidth reservation message having a requested quality of service, determining whether the network switching system has at least an available resource sufficient for the requested quality of service, and selectively increasing by the network switching system the requested quality of service in the data packet based on a determined absence of the available resource. The data packet is then output to the router based on the MAC destination address. The selective increase of the requested quality of service by the network switching system insures that the network switching system can control the bandwidth reservation process between the host computer and the router, without the necessity of establishing any messaging protocol between the host computer and the network switching system, or between the network switching system and the router. Hence, the network switching system can transparently control the bandwidth reservation process as needed without any modification to the bandwidth reservation protocol, the host computer, or the router.
Another aspect of the present invention provides a network switching system including an integrated network switch and a processing unit. The integrated network switch includes a plurality of network switch ports, at least one of the network switch ports configured for detecting within a data packet a bandwidth reservation message having a requested quality of service, the data packet received from a host computer. The integrated network switch also includes switching logic configured for identifying a second of the network switch ports for outputting the data packet to a router based on a corresponding media access control (MAC) destination address, and logic for selectively increasing the requested quality of service in the data packet. The processing unit is configured for controlling the logic to increase the requested quality of service in the data packet based on a determined absence of available resources within the integrated network switch sufficient for the requested quality of service. The determination by the CPU of whether the integrated network switch has a resource available that is sufficient for the requested quality of service insures that the integrated network switch is not overwhelmed due to the granting of the bandwidth reservation message by the router.
Additional advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the present invention may be realized and attained by means of instrumentalities and combinations particularly pointed in the appended claims.